Why do we sample vectors from a standard normal distribution for the generator?
It has become our human bias that data will arrive from a normal distribution. It is also the most prevalent distribution in nature occurring in many places. Hence, we sample from a normal distribution. Also, central limit theorem works around means lying around normal distribution.
It is not taboo to use others if they are helpful to your network. But, a data from one distribution can transformed into other and if that is something that is required, the network will to do it since it can approximate anything (although a weak assumption, but, hey, its working right?).